ABSTRACT
Objective@#To analyze the molecular typing characteristics by pulsed field gel electrophoresis (PFGE), drug resistance and virulence genes of Salmonella typhimurium in Longyan city in order to provide reference for the prevention and control.@*Methods@#A total of 79 Salmonella typhimurium strains were isolated from sporadic cases of diarrhea and food poisoning and raw poultry meat samples during 2010 to 2017. PFGE was performed to measure the minimum inhibitory concentrations (MIC) of 15 commonly used drugs against them. PCR was used to detect nine virulence genes (sopB, invA, sifA, sscA, sseE, spvB, pefA, spvR, spvC) in 55 strains.@*Results@#The 79 Salmonella typhimurium strains belonged to 61 PFGE types. There were 10, three and four strains of P1, P3 and P21 types, respectively. Seven P1 type strains were isolate from one food poisoning event. According to the 85% classification standard, 79 Salmonella typhimurium strains could be divided into five predominant gene clusters (G1-G5). Drug susceptibility test showed that the 79 strains had the highest resistance rate to ampicillin (88.61%), followed by that to tetracycline (87.34%) and streptomycin (73.41%). Multidrug resistant bacteria resistant to three or more antibacterial drugs accounted for 84.81% (67/79). All of the 55 strains carried invA, sopB, sseE and sscA genes. The other five genes, sifA, spvC, spvB, spvR and pefA, were detected in 54, 31. 10, 11 and 12 strains, respectively. There were 76.4% (42/55) of the strains carrying five or six virulence genes and all were positive for invA, sopB, sseE, sscA and sifA, and negative for spvB, spvR and pefA. The strains carrying all of the nine virulence genes accounted for 18.2% (10/55).@*Conclusions@#Salmonella typhimurium strains isolated in Longyan city had a diverse PFGE type. P1, P3 and P21 types were the three predominant PFGE types. In the food poisoning event, PFGE molecular typing could quickly alert the outbreak and traceability of Salmonella typhimurium. Attention should be paid to the multidrug resistance in Salmonella typhimurium. Monitoring of multidrug-resistant strains and supervision on antibacterial drug usage should be strengthened. Salmonella typhimurium had high virulence as it carried many virulence genes.
ABSTRACT
Objective To analyze the pulse-field gel electrophoresis (PFGE) patterns and antibiotic resistance of Salmonella enteritidisstrains isolated in Longyan city in order to provide reference for effective control, clinical diagnosis and treatment of outbreaks of food-borne diseases.Methods Seventy-seven Salmonella enteritidis strains isolated from food poisoning cases, livestock and poultry meat samples collected for food safety risk monitoring and sporadic cases in 2014 and 2016 were analyzed by PFGE.Antibiotic susceptibility testing was carried out to determine the minimum inhibitory concentrations (MIC) of 16 common antibiotics to 57 strains.Results Seventeen PFGE types were identified among the 77 Salmonella strains including three predominant types (P4, P6 and P8) and were grouped into three major pulsotypes (Cluster1-3) at 90% similarity level.The predominant types causing outbreaks of Salmonella enteritidis infection were P8, P6, P4 and P14, which were responsible for five cases of food poisoning.These isolated strains were highly resistant to nalidixic acid (93%), followed by resistance towards ampicillin (74%) and streptomycin (54%).Forty-one strains were resistant to three or more antibiotics (71.93%).Conclusion The PFGE types of Salmonella enteritidis strains isolated in Longyan city exhibit polymorphism and are clustered into three major pulsotypes.PFGE molecular typing can provide early-warning of sporadic outbreaks and help to identify the sources of infections in Salmonella enteritidis-related food poisoning.Attentions should be paid to multidrug resistant Salmonella enteritidis.Surveillance for multidrug resistant strains and usage of antibiotics should be strengthened.